The present invention relates to a device for cooling a turbine casing of a turbomachine, particularly an aviation turbojet engine or turboprop.
A turbine of this type comprises several stages each including a distributor formed of an annular row of fixed vanes borne by the casing of the turbine and an impeller mounted to rotate downstream of the nozzle assembly in a cylindrical shroud formed by ring sectors fixed circumferentially on casing hooks of the turbine via C-shaped or U-shaped fasteners.
The vanes of the first-stage or upstream-stage nozzle assembly are exposed to high temperatures and comprise internal cavities for the flow of cooling air bled off upstream from the turbomachine compressor and carried by ducts to a volume formed in the casing around the turbine upstream nozzle assembly. Cylindrical connecting tubes are mounted in the volume and each connect the volume to an internal cavity of a vane of the upstream nozzle assembly. The cooling air leaves this cavity at the radially internal end of the vane, the trailing edge of which may also comprise orifices opening into the cavity so that the cooling air can leave.
The hooks that secure the ring sectors, and especially those located directly downstream of the vanes of the upstream-stage nozzle assembly are shielded from the heat by an annular sealing plate which is mounted between the ring sectors and the external ends of the vanes of the nozzle assembly in order to restrict the passage of gas from the airstream radially outward into an annular space that houses the casing hooks.
However, sealing is imperfect and leaks of hot gases from the turbine airstream may cause the temperature of the casing hooks to rise and cause cracking or fissuring liable to destroy the hooks.
Furthermore, it would not be possible to fit the turbine with an additional cooling circuit leading cool air bled off upstream of the combustion chamber onto these suspension hooks because of the complexity, limitation on space and costs involved.